88 lines
4.0 KiB
Markdown
Executable File
88 lines
4.0 KiB
Markdown
Executable File
---
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author: Akbar Rahman (20386125)
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date: \today
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title: MMME3085---Lab 1 Coursework
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tags: [ mmme3085 ]
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uuid: 864e5249-a02c-4896-b274-a0a76789955c
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---
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\maketitle
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\newpage
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# Questions
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## Question 1
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- $V_{ref} = 5$ V when converting the ADC-converted value because the ADC in the Arduino can read
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from 0 V to 5 V, therefore $n_{ADC} = 0$ means the voltage to the pin is 0 V, and $n_{ADC} = 1023$
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means the voltage to the pin is 5 V
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- This is not the optimum use of the ADC pin as it means the resolution of the voltage measurement
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is less precise than it could be (roughly a resolution of 5 mV instead of 3 mV)
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- The resolution could be increased by using an op-amp amplification circuit or a 3.3 V to 5 V level
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converter circuit
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\newpage
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## Question 2
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- 100 % duty cycle PWM is different from all the others as it is not a wave, but just a DC voltage
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(the entire region is the ON region, hence it is not underlined in the figures)
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- Voltage is not zero in the OFF region because the rotational inertia is still spinning the motor,
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which creates a back EMF, and that is the voltage being read in the OFF region.
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Back EMF is proportional to the speed of the motor, which is why the voltage in the off region is
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higher when the PWM duty cycle, and therefore speed of the motor, is higher.
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\newpage
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## Question 3
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- The difference between the ON+ and ON- in the figure above is that the current will go in opposite
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directions, resulting in the motor spinning in opposite directions
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- The default PWM frequency of pin 13 on the Arduino Mega 2560 is 976.5625 Hz [^1]
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- The audible frequency we hear is a ~1000 Hz square wave, which can be seen by the fact the period
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of the wave in figure below is roughly 1 millisecond (see figure below)
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{ height=2in }
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\newpage
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## Question 4
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{ height=2in }
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{ height=2in }
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\newpage
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## Question 5
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- Since the internal timer only looks at one edge of one pulse, it cannot be used to determine the
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direction of the rotation, which is one of the reasons to use a quadrature in the first place
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- Therefore it is a viable alternative if you only care about the speed of rotation and direction
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is not important to the application
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## Question 6
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- The main shortcoming observed is that the Arduino appeared to freeze/crash when entering a PWM
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duty cycle above ~20%
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- When this issues occurs, the Arduino is too busy running the function called by interrupts
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to be able to print to serial, hence appearing to have frozen/crashed
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- This is due to the fact that at higher speeds, the `updateEncoderStateMachine()` function in
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triggered by the digital pin interrupts (which take higher priority) so frequently that
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the `loop()` function is not able to run, due to a lack of free CPU cycles, and therefore serial
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outputs are not printed and inputs not read
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- This effectively makes the counter useless as it cannot be read from as the Arduino is not able
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to handle any other processing tasks
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- Additionally, there is a good chance that the Arduino is not able to run all the calls to
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`updateEncoderStateMachine` in real time, and so the value of `count` would be incorrect (of course
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this does not matter since we do not have the CPU cycles to do anything with `count` anyway)
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[^1]: `MotorEncoderAAR.ino` defines that pin 13 is used for PWM output. Pin 13 is connected to timer 0 which defaults to 976.5625 Hz (<https://playground.arduino.cc/Main/TimerPWMCheatsheet/>)
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